README: Replace broken mailing list link with archive (#543)

Co-authored-by: Łukasz Langa <[email protected]>

Author: hugovk

README.rst

@@ -144,7 +144,9 @@ which can be found on PyPI.
 Questions?
 ----------
 
-There's a mailing list available for support on Google Groups,
-`html5lib-discuss <http://groups.google.com/group/html5lib-discuss>`_,
-though you may get a quicker response asking on IRC in `#whatwg on
-irc.freenode.net <http://wiki.whatwg.org/wiki/IRC>`_.
+Check out `the docs https://html5lib.readthedocs.io/en/latest/`_. Still
+need help? Go to our `GitHub Discussions
+https://github.com/html5lib/html5lib-python/discussions`_.
+
+You can also browse the archives of the `html5lib-discuss mailing list 
+https://www.mail-archive.com/[email protected]/`_.